Hybrid electric vehicles include a vehicle traction motor in addition to an internal combustion engine. The electric motor is connected to at least two wheels by a transmission or gearbox. The motor provides output torque to the wheels through the gearbox for propelling the vehicle. The may motor also receive input torque from the wheels through the gearbox for generating electricity and braking the vehicle (regenerative braking). Electric vehicles often include a braking system that utilizes both friction braking and regenerative braking. Regenerative braking is used to recharge vehicle batteries, and recovers much of the energy that would otherwise be lost as heat during friction braking. Therefore regenerative braking improves the overall efficiency or fuel economy of the electric vehicle as compared to vehicles only configured for friction braking.
During regenerative braking, interactions between an antilock braking system (ABS) of the vehicle, the powertrain and the road surface can result in deflections in the powertrain (i.e., powertrain oscillations). Consequentially, during an ABS event regenerative braking is disabled to avoid destabilizing the vehicle.